Category Archives: Research review

In this post, I’ll discuss some of the results of the study I described in my previous post. If you haven’t already done so, you should read that one before this.

To refresh your memory, Santaella and his colleagues studied the effects of bhastrika practice in elderly individuals (1). They tested several measures of respiratory function at the beginning of the study and again after four months of training. Those measures included forced vital capacity (FVC), forced expiratory volume in one second (FEV1), and maximum expiratory and inspiratory pressures (PEmax, or MEP, and PImax, or MIP). Don’t worry about the abbreviations. Scientific research tends to read like acronym soup, but in general I’ll stick to the full names.

Breathe in as much as you can, then exhale out as much as possible. The amount of air you exhaled is your forced vital capacity. You’ll never empty all the air out of your lungs, so vital capacity doesn’t represent your lungs’ total capacity, but it’s a good measure of their useable capacity.

The air that’s left in the lungs after a complete exhalation is called the residual volume. Residual air is important. It helps to maintain a moist, carbon dioxide-rich atmosphere in the lungs and allows for continual gas exchange even after you’ve exhaled.

Vital capacity is a function of the size of your lungs, which is correlated with the size of your body, particularly your height. It’s also a function of your age. As you grow older, your lungs lose elasticity and your chest becomes stiffer. This leaves more air trapped in the lungs, increasing the residual volume, which leads to a gradual decline in vital capacity.

Now do the same exercise, breathing in and out as much as possible, but try to exhale as quickly as you can. The amount of air you exhale within the first second is called forced expiratory volume in one second, or FEV1. You may have done this test in your doctor’s office. FEV1 is an important measure of the health of your lungs. If you’re healthy, you should be able to empty out 80% or more of your vital capacity in the first second. If you can’t, because there’s some obstruction to the air flow, it could be a sign of asthma, chronic bronchitis or emphysema.

Maximum inspiratory and expiratory pressures are self-explanatory. They are measures of the maximum pressure you can generate while inhaling and exhaling through a mouthpiece. Both of them are indirect measures of the strength of your respiratory muscles.

The elderly lose both muscle mass and strength as they age, a process called sarcopenia. Exercise does a lot to mitigate sarcopenia, but some loss seems to be inevitable. Not surprisingly, as the strength of the respiratory musculature declines, maximum inspiratory and expiratory pressures also decline. That can be a serious problem for the elderly when conditions such as pneumonia place an extra load on the respiratory muscles. Since vital capacity and respiratory pressures decline with age, anything that improves them would be good news for the elderly.

So, did bhastrika practice help? The results were mixed. Maximum inspiratory and expiratory pressures improved significantly in the bhastrika group. Forced vital capacity and FEV1 increased slightly in the bhastrika group, but the difference was not statistically significant. The control group remained essentially unchanged, despite the fact that they were also practicing yoga (but without the bhastrika practice).

Research has generally shown that you can’t improve vital capacity with exercise. (On land at least. Swimming does increase vital capacity, probably because of the greater resistance to breathing that water provides.)

Some research suggests that yoga practice can improve vital capacity, but there are enough weaknesses in those studies that I’m not convinced. Most of the evidence comes from uncontrolled studies on students who were teenagers or young adults (2, 3). Women don’t reach full vital capacity until around age 20. For men, it’s around age 25. Without a control group, it’s hard to know whether those young people’s vital capacity would have increased regardless of yoga training. One large uncontrolled study (3) of college students did find increases across the board, regardless of age and gender. That’s suggestive of a training effect, but aside from the lack of a control group, there was also enough room for error in the testing procedures that those results aren’t as compelling as they could be.

I’ve only found one controlled study (4) showing a link between improved vital capacity and yoga. Unfortunately, there were major differences in the composition of the experimental and control groups in that study, and no details about the selection process, so again, I’m cautious about the results.

Other studies have found no correlation between yoga practice and vital capacity. It would be nice if there were better-designed studies to answer the question, especially for mature adults, but for the time being I’m not convinced that yoga does much to increase vital capacity. If it does, my guess is that the effect is small, unless you’re young. In that respect Santaella’s results weren’t surprising.

On the other hand, maximum inspiratory and expiratory pressures are a function of muscle strength. You can strengthen muscles, so you’d expect those measures to improve with training, and, in fact they did in this study. Overall, there hasn’t been much research on this topic. What little there is suggests that yoga practice can increase inspiratory and expiratory pressures (5), although in one of those studies (6) the difference was not statistically significant.

The bhastrika practice in this current study consisted of rounds of kapalabhati followed by breath retentions incorporating bandhas. I’ve written about kapalabhati before. It’s a strengthening exercise for the expiratory musculature, specifically the transversus abdominis as well as other abdominal muscles.

Inhalation retentions, particularly using jalandhara bandha, strengthen the muscles of inspiration. Jalandhara bandha is the “net-holding lock,” sometimes called chin lock. It requires you to hold the ribcage in a lifted position while bringing your chin towards your sternum. At some point, I’ll write about the physiological rationale for jalandhara bandha, but for now I’ll just point out that maintaining the position of the ribcage necessitates a strong contraction of the external intercostals along with the scalenes and the diaphragm, all of which are muscles of inspiration.

So, for the elderly individuals in this study, bhastrika practice seems to have strengthened their respiratory muscles. I should point out one caveat, though. The researchers in this study tested their subjects first to make sure they were healthy, and did not include any with evidence of cardiovascular disease in the study. Both kapalabhati and breath retentions can affect blood pressure. Because high blood pressure is common in the elderly, I wouldn’t recommend that senior citizens practice them unless they have a physician’s approval.

In the next post in this series, I’ll discuss the findings relating to heart rate variability.

You don’t need to know anything about science to practice yoga. The ancient yogis didn’t. Their method was introspection. They discovered the effects of yogic practices through sustained attention to their own internal physical and mental states. Given how much variation there is between individuals, that’s probably still the best way for you to determine the effects of your own practice.

However, yoga and meditation also teach us how untrustworthy our interpretation of things can be. We see what we want to see. Patanjali describes it in the Yoga Sutras as viparyaya—misconception.

One of the fundamental ways we are primed by evolution to mis-conceive is to see causality where none exists. “I practiced headstand, and my headache went away, so headstand much have cured it.” Not necessarily. Just because two events are correlated doesn’t mean one caused the other. And even if it did, that doesn’t mean it would work for anyone else.

A lot of scientific studies simply find correlations. That’s particularly true in epidemiological research, where scientists look at large populations to discover things like “people who drink coffee have higher rates of depression.” (I’m just making that up. I don’t know if there’s any such study.) The media often report those studies with headlines like “Coffee causes depression.” Well does it? Maybe. But maybe not. We can’t tell, because it’s simply an association. Correlation doesn’t prove causality. At most, it can generate hypotheses, which then have to be tested.

From a scientific point of view, the only way to demonstrate causality is in a randomized controlled trial. Take two groups of randomized individuals, who—in theory—don’t differ in any significant way. Test each group at the beginning of the experiment, then give one group some sort of experimental treatment with the other group acting as a control. Re-test everybody at the end. Assuming that the only difference between the groups was the treatment you gave—which is a very big assumption—any change in the experimental group had to have come from the treatment. However, this process can go wrong in all sorts of ways, which is why one trial doesn’t prove much of anything. In fact, to be accurate, no amount of trials can prove anything. All a scientific trial can really do is disprove a hypothesis. There’s always the possibility that another, unidentified factor caused the results we see, and not the experimental treatment.

Hopefully, that wasn’t too basic an introduction to the scientific method, but, since I plan to periodically review yoga research here, I wanted to cover the background first. The main point is that scientific studies vary in quality. Unfortunately, much of the yoga-related scientific literature is not very compelling. Many studies are poorly designed, or else so poorly reported that it’s hard to interpret their results—which amounts to the same thing from a scientific point of view.

This study, however, was well designed and reported, so I’m hoping it can serve as an example of what to look for in scientific research. Plus, you don’t have to rely on the abstract. You can read the full text here. It’s free, unlike many studies that require you either to be a subscriber to the journal or to pay an exorbitant fee to read the full text.

Anyway, on to the study. Investigators in Brazil hypothesized that practicing “bhastrika” would improve respiratory and autonomic nervous system function in healthy senior citizens. I put “bhastrika” in quotes because, while the term comes up a lot in pranayama research, it seems every researcher uses it to mean something different—probably because different schools of yoga define it differently. In this case, they mean kapalabhati with surya bhedana: 45 kapalabhati breaths, followed by an inhalation through the right nostril, a retention with bandhas, and a long, slow exhalation. (There’s a video here.)

This was a randomized controlled trial, which is generally the highest quality study design you’ll find in yoga research. (You’ll almost never see “blind” or “double blind” randomized controlled trials, which are the scientific gold standard, because it’s pretty obvious whether you’re doing yoga or not. Some studies have had control groups do “sham” yoga as a way of blinding participants as to which group they’re in, but that’s generally unconvincing.)

The groups were small, with 15 participants in the experimental group and 14 in the control. Those are pretty typical numbers for exercise training studies, because it’s expensive and difficult to recruit larger groups.

On the other hand, if the groups are too small, a few random outliers could mask an effect that’s actually there, so researchers need enough participants to ensure what’s called statistical power. It’s a good sign in a study when the authors include an analysis of statistical power, as they do here.

The authors provide a flow chart that gives some insight into the difficulties of recruiting subjects for these kinds of studies. They began with a pool of 150 participants in a yoga program for the elderly. Only 76 people volunteered for the experiment. Of those, 46 were excluded for health reasons such as cardiovascular disease, or because they were taking medications which could affect the results. That left 30 people, or two groups of 15. (One person in the control group didn’t attend the required classes and was dropped from the experiment.)

The authors also list demographic and biochemical statistics for the two groups to show that there weren’t obvious significant differences between them. If there were big differences, say one group were significantly older or had more men or women, those could affect the results. Randomization is supposed to eliminate such differences, but it doesn’t always, so it’s a good sign when researchers check. Of course, there could be other important differences they overlooked, but nevertheless, it’s a good sign.

Everyone in the study participated in an hour-long yoga asana class twice a week for four months. The experimental group followed that up with an extra half-hour of training in bhastrika, while the control group did 30 more minutes of asana. The experimental group also practiced bhastrika twice a day on their own for 10 minutes at a time, recording the sessions in a diary to verify compliance.

Most yoga studies have focused on the effect of a comprehensive practice that often includes asana, pranayama and meditation, and even lifestyle and dietary changes. That’s useful because it tells us something about the overall benefits of a yoga practice, but it doesn’t say anything about what specific exercises do. Was it the asana or the meditation that made a difference? We don’t know.

To me, the most interesting aspect of this study is that the authors chose not to do that, instead opting to test the effects of one specific practice. Everyone, both the control and the experimental subjects, did essentially the same yoga practice. The difference was that the experimental group added bhastrika. Therefore, we can expect that any differences in the results we see between groups will—probably—be due to bhastrika.

Participants were tested at the beginning of the study and again at the end. Those tests included measures of respiratory function, autonomic nervous system balance, and quality of life. I’ll wait to describe those in more detail over the next couple of posts because I also want to explore some of the underlying physiology along the way.

Part two of this series will look at how the bhastrika practice affected participants’ respiratory function.